This page explains how to find the radius of given circle if you know its area. You can print cool lessons and worksheets to practice the concept....

Steps towards learning how to find the area of any circle:

Before learning how to find the area of a circle let's understand the concept of surface area or simply area.

Area is the surface enclosed in the closed boundaries and these boundaries can be square in shape, rectangular or circular or any other shape.

The key to find the area of any shape is the square shape with a unit length (or unit squares). To find the area any other kind of shape that shape is filled with these unit squares and then these squares are counted to find the area of the shape.

For example; consider there is a rectangle with a length of 10 cm and width of 5 cm as shown below:

Now the above rectangle can be filled with 50 unit squares of side length 1 cm. So the area of the rectangle will be 50 centimetre squares.

Similarly area of the circle can be found by drawing small unit squares inside the circle, but the problem will be the circular boundaries of this shape. As a result we can't fit exact number of squares inside a circle. See the picture given below:

From the above figure it is clear that we can't find the exact area of a circle because we can't fit exact number of squares inside a circle. But still we can give a good estimate of the area of the above circle by counting the full squares and half squares inside it.

Hence we need a consistent and easy method to find the area of a circle. So the mathematicians develop a formula to find the area of any given circle.

You need to know about the diameter of a circle then its radius and finally a constant pi.

The longest chord of the circle is called its diameter or any chord of the circle going through its centre is called the diameter.

Half the length of the diameter is called the radius.

The ratio of circumference of a circle to its diameter is always constant and is called pi. Its value is 3.14 (To 2 decimal places).

Lessons and worksheets on how to find the area of a circle

Print the following area of circle worksheet ex planing how to find the area of a circle when its radius (r) is given.

(click on worksheets to print it)

Print the following worksheet to teach kids about how to find the circle area when its diameter is given.

Different Ways To Find The Area Of A Circle:

There are a number of ways to find the area of a given circle. Following are the most important methods used to find the circle area in different circumstances.

1. Area of a circle when its radius is given:

The most important method to find the area of any circle is using its radius. There is very simple formula to find the area of a circle when its radius is given. This formula use the constant pi and radius.

This method is very very easy to understand and grade six students can learn it very easily by looking at solved examples.

So, let's learn this basic method to find the area of any circle when its radius is given by using the following example;

Find the area of a circle whose radius is 6 cm.

Simple, isn't it. Now you can solve same kind of problems with any different value for the radius. The basic to find the area of a circle, when its radius is given, is "pi times radius times radius". Just remember this and you will be excellent to solve all kinds of problems when radius is given.

For any given radius of a circle you can find its area by using your calculator very easily. On your calculator multiply 3.14 to radius squared or 3.14 x radius x radius.

2. Finding area of a circle from its diameter

The second method to find the area of a circle is using its diameter. Sometimes the radius of the circle is not given but its diameter. But these both parameters are very closely related.

Kids need to remember that diameter is twice the radius of the circle. In other words, we can find the radius of the circle by dividing the diameter by 2 and then use the same formula to find the area.

Some teachers use diameter in the formula to find the area but we suggest our students to use only one formula to find the area of all the circles and this formula is pi times radius squared. Let's do another example to understand the second method to find the area of a circle.

Conclusion:

Finally we can conclude that the area of a circle can be obtained from its radius or diameter, but it is a good practice to use only one parameter (radius or diameter) in the formula and radius is preferred.

In other words even if the diameter of the circle is given, convert it into the radius by dividing its value by 2 and then use the same formula to find the area all the times.

Now you can solve some of the similar problems on finding area of a circle when its radius or the diameter is given.